The invention relates to a stress test rig for helicopter transmissions.
In DE 196 16 729 A1, a generic stress test rig has been disclosed. One test rig transmission, driven by a motor, is operatively connected via shafts and connecting couplings with a helicopter transmission to be tested which has a rotor shaft on the output side. Situated above the rotor shaft of the test transmission, a second test rig transmission is operatively connected with the rotor shaft. A combination of shafts connecting to the first test rig transmission completes the stress circuit. A stress mechanism is provided for predetermining the stress torque in the stress circuit. By the feedback of power from the test transmission output to the test transmission input, high testing powers are made possible without a correspondingly high expenditure of energy, since only power losses must be applied by the motor in the stress test rig.
During rotation speed reductions, helicopter transmissions branch input powers from one to three prime movers to different outputs like main rotor, rear rotor and auxiliary outputs. The specifically highly stressed transmissions are small and light in design according to the requirements in air travel. The housing are mainly made of aluminum and magnesium alloys. The elasticity modules of the materials are from one half to one third of the elasticity module of steel alloys, i.e. the elastic deformations are accordingly larger under load. A torsion of the transmission housing around the rotor shaft axis particularly occurs.
The consequence of this is that inputs or outputs which are disposed on the transmission at a radial distance from the rotor shaft axis, shift from an initial position. Opposite to the axes of attachable shafts, which lead to the prime movers or to the rear rotor output, the axes of the inputs and outputs of the transmission gearings and radial displacements occur.
In the helicopter, part of this displacements is compensated by non-torsional, angularly movable discs or diaphragm couplings. But a considerable part of the displacements are compensated by the connecting shafts, very long as a rule, leading to the prime movers or to the rear rotor output.
When the transmission is installed in such a stress test rig, the installation situation of the transmission is extensively simulated in the helicopter cell. For reasons of technical economy and space, however, substantially shorter input and output shafts are being used.
On account of the short shafts, a large part of the displacements must be compensated by the coupling elements. Together with substantially high load of the coupling elements due to the large angles, there also appear on the input and output shafts of the helicopter transmission substantially high bearing loads in a radial direction. The heavy loads simultaneously with very high rotational speeds of up to about 25,000 1/min (revolutions per minute) can result in destruction of the coupling elements and damage to the supporting range of the input and output points and on the highly sensitive free wheels of the helicopter transmission. But the stresses in the test rig must not exceed the operating loads on the helicopter or, in the worst case, cause damage to the transmission.
U.S. Pat. No. 5,207,676 has disclosed a gear cutting test machine having devices for position changes of the individual gear wheels geared with each other.
The problem on which the invention is based is to further develop a generic stress test rig so that, as exact as possible, a simulation of the loads appearing on the helicopter is made possible in a small space. The stress test rig must be flexibly adaptable to different types of helicopter transmissions and load profiles, and operate safely within admissible loads or damages.
The problem is solved by the fact that a clamping plate, rotatable by at least one actuator around the rotor shaft axis of the test transmission, is provided for supporting the test transmission. The arrangement makes it possible, wholly or partly, to compensate for the displacements appearing under load on the connecting couplings of the test transmission.
In an advantageous development of the invention, the rotatable clamping plate and the actuators are situated on an assembly truck which accommodates the test transmission and all necessary adaptation devices, e.g. adaptative transmissions. In connection with this invention, the use of an assembly truck offers the advantage that with simple means an individual adaptation for different types of helicopter transmission is possible. The connecting points for transmission bottoms or bottom flange of the test transmission are situated in the clamping plate so that the axis of rotation of the clamping plate coincides at least approximately with the rotor shaft axis. The arrangement of the clamping plate of the actuators and, if needed, the required adaptation transmission on the assembly truck makes possible a standardized connecting point of assembly truck to test rig.
An advantageous arrangement of the actuators results when two symmetrically opposite actuators are provided, each of which is situated tangentially to the direction of rotation of the clamping plate between a connecting point on the clamping plate and a connecting point on the assembly truck. By virtue of this arrangement, the support of the rotatable clamping plate on the assembly truck remains at least approximately free of radial forces.
Stresses can be avoided by an axially movable support of the clamping plate in a direction along the axis of rotation.
In an advantageous development of the invention, the stress mechanism has a stress motor with an electric stress torque regulator unit controlled by a microprocessor and an overlay transmission. The stress-torque dependent control of the actuators is simplified, especially when an electronic actuator-control regulator unit with a signal input for theoretical stress torque value and at least one signal output for a theoretical position value of an actuator or of the clamping plate is provided.
On account of the short shafts, a large part of the displacements must be compensated by the coupling elements. Together with substantially high load of the coupling elements due to the large angles, there also appear on the input and output shafts of the helicopter transmission substantially high bearing loads in a radial direction. The heavy loads simultaneously with very high rotational speeds of up to about 25,000 1/min (revolutions per minute) can result in destruction of the coupling elements and damage to the supporting range of the input and output points and on the highly sensitive free wheels of the helicopter transmission. But the stresses in the test rig must not exceed the operating loads on the helicopter or, in the worst case, cause damage to the transmission.
Great security can be obtained when in the stress circuit at least one torque sensor is situated and the electronic actuator-control regulator unit has at least one signal input for an actual value of the stress torque of the torque sensor or when at least one sensor is provided for the actual position value of an actuator or of the clamping plate.
The invention is shown in detail with reference to the drawings wherein:
FIG. 1 is a diagrammatic top view on one part of a stress test rig known already;
FIG. 2 is a diagrammatic top view of one part of an inventive stress test;
FIG. 3 is a diagrammatic side view of one part of an inventive stress test rig; and
FIG. 4 is a diagrammatic representation of the control of the stress test rig.